It is known to provide feedback circuits in analyzers which alter in real time the output of illuminating devices, depending upon the level of signal detected at the detector. An example of such a system is shown in U.S. Pat. No. 5,491,329, which uses the irradiation on in vivo tissue samples. Such tissue samples of course are not known in advance as to their photoresponse efficiencies. Furthermore, the reason for the feedback circuit in such a system is to allow the proper use of the gain on the photomultiplier tube used in the detector. Such a use is irrelevant to detectors using flash lamps and simple photodiodes.
Yet another example of a real-time adjustment of the exposure device to reflect the system efficiencies of the optics is disclosed in U.S. Pat. No. 5,029,245. In this case, LEDs are modified during sample examination so that the radiation outputted is "regulated in accordance with the intensity data supplied [in real time] by the detector and in such manner that the radiation intensity of that wavelength range, and thus the intensity of the output radiation, is constant," column 4, lines 10-14.
Other examples of analyzers that adjust a lamp intensity depending upon the sample transmission detected in real time at a detector, but not preselected before exposure, are shown in, e.g., Research Disclosure Publication No. 40001, dated August 1997.
Although real-time adjustments are useful, they have the disadvantage of requiring fairly complex and sensitive optical systems, given the wide range of possible outputs and the lack of a priori control of outputs. Also, real-time adjustments necessitate some delay in the assay while changes are made in response to the reading, compared to the time needed for assays that have predetermined settings selected in advance. Furthermore, those that adjust simply on the basis of an instantaneous result do not provide any adjustment based on known performances of that particular assay as a whole.
Thus, there has been a need for a method of making energy level adjustments to illuminating devices in advance, for testing end-point assays selected from a list having known end-point photoresponse efficiencies, exposed in an optical system having a known system efficiency, without necessitating the complexities required for real-time adjustments.
As used herein, "photoresponse efficiencies" means, efficiencies dictated by the end-point photoresponsiveness of the chemistries used for a particular assay, and more specifically, the photoresponse that is determined from a plot of the photometric end-point density produced by the assay versus concentration of the analyte of that assay. In such plots, the steeper the curve, the more efficient is the photoresponse, and the less intense must be the illuminating device to obtain a satisfactory reading.